If angle A = 120°, what is angle B? Explain. If angle D = 40°, what is angle E? Is your reasoning the same? If the sum of angle B, angle C, and angle D is 180°, what is angle C?

Angle A and B are supplementary: both form a 180° angle.
So, if A=120° , then B=180°-120°=60°.
Angle D and E are also supplementary and form a 180° angle.
If D=40°, then E=180°-40°=140°.
The reasoning is the same that for the previous pair of angles.
The sum of the interior angles of a triangle is equal to 180°, so we can write:
[tex]\begin{gathered} B+C+D=180\degree \\ C=180\degree-B-D \\ C=180\degree-60\degree-40\degree \\ C=80\degree \end{gathered}[/tex]Answer:
B=60°
E=140°
C=80°